Tapered piles and methods of using tapered piles

ABSTRACT

A molded concrete tapered piling which is reinforced or prestressed and has a preferred amount of taper per unit length of piling, and method of using said piling by driving it into earth stratas including stratas wherein it has been found that straight-sided pilings of comparable length do not provide sufficient load-bearing capacity, lateral support and uplift anchorage for a structure to be built thereon.

United States Patent [191 Medema [75] Inventor: William H. Medema, Fort Lauderdale, Fla.

[73] Assignee: Oolite Industries, Inc., Miami, Fla.

[22] Filed: Nov. 1, 1971 [21] Appl. No.: 194,109

[52] US. Cl. 61/56, 61/50 [51] Int. Cl EOZd 5/30, E02d 27/12 [58] Field Of Search 61/56, 53, 53.5, 56.5

[56] References Cited UNITED STATES PATENTS 722,417 3/1903 Villet 61/56 1,257,835 2/1918 Ferguson 61/56 2,065,507 12/1936 Alexander 61/56 2,187,316 1/1940 Greulich 61/53 2,187,318 1/1940 Greulich 61/56 2,645,090 7/1953 Kinneman 61/56 2,759,332 8/1956 Lloyd 61/56 June 28, 1974 FOREIGN PATENTS OR APPLICATIONS 230,436 1/1911 Germany 61/56 OTHER PUBLICATIONS Concrete Piles, Design, Manufacture, Driving pub. by Portland Cement Assoc. receive in P0. 1938, pages 25, 27, 28.

Primary Examinerlacob Shapiro Attorney, Agent, or Firm-Stevens, Davis, Miller &

Mosher ABSTRACT A molded concrete tapered piling which is reinforced I wherein it has been found that straight-sided pilings of comparable length do not provide sufficient loadbearing capacity, lateral support and uplift anchorage for a structure to be built thereon.

9 Claims, 5 Drawing Figures PATENIEDmza lam H FIGJS FIG.3

TAPERED PILES AND METHODS OF USING TAPERED PILES BACKGROUND OF THE INVENTION This invention relates in general to piles and methods of using piles, and more specifically to a novel pile having tapered longitudinal sides, and a method of using this novel pile.

In the construction industry, the use of piles which are driven into earth, rock, or lake, river, or ocean beds, to provide load bearing supports for structures to be constructed thereon, is well known. Piles or pilings are typically driven with their longitudinal axes in vertical orientation to a point of refusal commensurate with designated criteria. Such piles also provide uplift support and stability to firmly anchor structures built thereon against the potentially destructive forces of wind, currents or waves.

For various applications, piling may be constructed of any suitable material including wood, metals, or hardened compositions such as concrete. When formed and hardened compositions, such as concrete, are used, piles may be reinforced or prestressed by well known methods. Because the function of piles is to provide underground support, piles are provided in simple and economical shapes which facilitate driving them into the earth strata upon and in which they are to support themselves. Piles typically comprise elongate, rigid, straight sided members having any suitable crosssectional goemetry, including circular, H- or l-shaped,

rectangular, square, or octagonal shaped crosssections, or any other suitably shaped cross-section.

Some piles have included one or more longitudinal surfaces wherein the surface was tapered with respect to the axis of the pile. For example, Greulich US. Pat. Nos. 2,187,316 and 2,187,318 illustrate varying pile constructions, including two or more tapered sides, and Deane U.S. Pat. No. 1,111,366 discloses a tapered hollow tubular pile. However, the straight sided tip portion of the Greulich piles will drive through firm soil or strata, thereby destroying effectiveness of the tapered portion in such strata, and the exposed metallic main body of the Greulich piles will deteriorate much faster than concrete.

Due to the variety of soil conditions in which piles are driven and in view of the variety of requirements such as load capacity, uplift capacity, length, cross-sectional area, material costs, driving costs, and others, including builing codes and other economic limitations, there remain a variety of applications wherein novel piles and novel methods of using piles may produce highly advantageous results. For example, in soil conditions where layers or strata of earth or rock which support pilings is at a great depth, extremely great and uneconornical lengths of pilings are required to support surface structures which are so heavy that the soil structure above the strong earth or rock layer will not itself support the surface structure. Consequently, enormous amounts of piling materials may be used to provide rigid support for the surface structure between the surface and the strong earth or rock strata, or other expensive techniques such as vibra-flotation or bulk concrete filling may be used to densify the substrata. n the other hand, where short pilings may be sufficient to provide adequate load-bearing support fora structure, the pilings may be so short and so unfirmly anchored in the earth as to not provide the sufficient uplift or lateral support to securely anchor the building against external forces such as wind, waves, or currents.

SUMMARY OF THE INVENTION It is, therefore, an object of this invention to provide piles and methods of using piles which overcome the aforementioned disadvantages and satisfy the aforementioned needs.

It is another object of this invention to provide a novel tapered pile.

It is another object of this invention to provide a molded concrete tapered pile.

It is another object of this invention to provide a reinforced and prestressed concrete tapered pile.

It is another object of this invention to provide a novel prestressed concrete tapered pile having adequate load bearing capacity, and which also provides adequate uplift support for structures built thereon.

It is another object of this invention to provide a prestressed tapered concrete piling which provides adequate load bearing capacity and uplift anchorage in earth strata where it has heretofore been impossible to provide such support with such short pilings.

It is another object of this invention to provide adequate load bearing capacity and uplift anchorage with pilings which are much smaller and much more economical than previous pilings which could provide the same load bearing support.

It is still another object of this invention to provide a piling which may be driven to a desired point of refusal more quickly.

It is yet another object of this invention to provide a novel method of using pilings to provide sufficient load bearing capacity and uplift anchorage to enable the building of structures on strata where it was heretofore impossible to build such structures with so little piling.

The foregoing objects and others are accomplished in accordance with this invention by providing a molded concrete tapered piling which is reinforced or prestressed and has a preferred amount of taper per unit length of piling, and methods of using said piling by driving it into earth stratas including stratas wherein it has been found that straight sided pilings of comparable length do not provide sufficient load bearing capacity and uplift anchorage for a structure to be built thereon.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention, as well as other objects and further features thereof, reference is made to the following detailed disclosure of preferred embodiments of the invention taken in conjunction with the accompanying drawings thereof, wherein:

FIG. 1 is a partially schematic, longitudinal section view of a tapered pile of the present invention;

FIG. 2 is a partially schematic, cross-sectional view of the pile of FIG. 1 along line II;

FIG. 3 is a partially schematic, bottom view of the tip of the-pile illustrated in FIG. 1; FIG. 4 is a partially schematic-isometric view of a structure supported by the piles of the present invention;

FIG. 5 is a partially schematic, cross-sectional view of a portion of the structure of FIG. 4, including the foundation and piling structure thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG; 1 illustrates a partially schematic, crosssectional view of the advantageous tapered pile of the present invention wherein the pile structure typicallycomprises a unitary structure having an upper straight-sided, butt portion 11, with sides which are substantially parallel to the axis 12 of the pile, and a top butt surface 13 which is substantially perpendicular to longitudinal axis 12.- The inventive pile also includes tapered tip portion 14 of the longitudinal surface of the pile, and said tapered tip portion commences at a shoulder 15 at the lower end of the straight-sided butt portion 11 of the pile. The tapered tip portion 14 is tapered toward the bottom 16 of the pile and the tapering is symmetrical about longitudinal axis 12. FIG. 1 also illustrates vertical unit length 17 and corresponding horizontal length 18 which define the amount of taper of each of the longitudinal tip surfaces is preferably in the range of about one-eighth to about three-eighths inch per foot of length (said length taken along or parallel to the longitudinal axis of the pile). This range provides a reduction of the total width of the pile in the range of about one-fourth to three-fourths inch per linear foot of pile in the tapered tip portion. A particularly preferred tapered pile has a total reduction in width of about one-half inch per linear foot, i.e., each surface converges toward the axis about one-fourth inch per linear foot.

Piles having much less taper are essentially straight sided piles, and behave accordingly, while piles having much greater taper typically do not provide sufficient uplift anchorage. When piles having these preferred amounts of taper are used in accordance with this invention, they provide the surprising and useful advantages discussed below herein. The straight sided butt portion 11 of the inventive pile has the same crosssectional dimension as the widest portion of the tapered tip portion of the pile, so that it provides the largest possible load bearing cross-sectional area, and also is adapted to fit the driving bonnet in commercially available pile driving equipment. The top comers of the butt surface 13 may be mitered to prevent chipping or spalling of the butt section during driving. The straight sided butt section also facilitates capping of the piles for attachment to the structure being built thereon, and the butt section may be capped intact, or cut off and then capped.

FIGS. 2 and 3 illustrate the preferred cross-sectional geometry of piles of the present invention wherein the piles have square cross-sections throughout their length, said square cross-sections being everywhere substantially symmetrical to the longitudinal axis 12 of the pile. Piles having substantially square cross-sections are easy to mold and are readily driven with commercially available pile driving equipment.

Also illustrated in FIGS. 1, 2 and 3, are the advantageous reinforcements which are used to reinforce and- /or prestress the molded concrete piles of the present invention. The reinforcing may comprise any suitable reinforcing material, and that illustrated in FIGS. 1 3 comprises longitudinal strands of steel wire or longitudinal bars arranged as illustrated in FIG. 2 in a square configuration on the diagonals of the square crosssectional shape of the pile, and extending throughout the length of the pile from the upper butt face 13 to the lower tip surface 16. These longitudinal strands are used in prestressing the concrete, andprovide the pile with internal support and increased elasticity. Transverse forces may occur during driving and while piles are stacked or are being moved or positioned for driving. The inventive piles may be specifically designed to withstand pick-up at one or more points along their length. Transverse reinforcements are illustrated in the straight sided portion 1 1 as a series of hoops 20 of steel wire reinforcement around and welded or otherwise secured to the longitudinal reinforcements 19. In an alternative embodiment, the transverse reinforcing material may be spirally wound around the longitudinal reinforcements as illustrated at 21 in FIG. 1. Only a portion of the transverse reinforcement material is'illustrated here, but it will be understood that the pile is transversely reinforced throughout its length. In the inventive tapered piles of length up to about 28 feet, conventional concrete reinforcing rebars may be used instead of wire reinforcements. In addition, the top of the butt section and the extreme tip section of the tapered portion of the pile may be heavily reinforced to provide additional support against the blows of the driving hammer and adequate penetration strength, respectively.

Concrete, and particularly reinforced and prestressed solid concrete, is a preferred material for pilings because it is not susceptible to chemical degradation and spalling off as are many other materials. Metallic reinforcements are sealed within the solid concrete thereby protecting them from degradation, for example by oxidation. Hence, the life of concrete pilings is substantially greater than the useful life of other materials which might be considered for use in pile construction.

Piles are typically designed for specific load capacity criteria, for example 35 ton or ton capacity, and in various embodiments various desired dimensions may be used for the various portions of the inventive pile. For example, the square cross-section of the straightsided butt portion may be of any desired area; however, the butt portion is typically designed in standard dimensions for use with bonnets of commercially available pile driving equipment. For example, molded concrete pilings having square butt cross-sections of 14 in. or 18 in. square, are often used for piles whose designed load bearing capacity is in the range of about 35 tons. Similarly, the length of the tapered portion and the length of the straight-sided butt section will vary depending upon the specific pile length desired for use in a specific construction site. The tapered side portions in the inventive pile are planar, and therefore the length of the tapered side portion is limited by the width of the widest portion of the pile and the width of the tip of the pile. If the width of the pile at the shoulder, as well as at the tip, have been determined, and the amount of tapering is determined, then only the length of the straight-sided section of the pile can be varied to vary the total length of the pile. In addition to the length of the pile which is driven below the surface, the length of the pile may be varied for use in capping the pilings and determining the elevation of the foundation which is secured upon the top of the pilings. As already stated hereinabove, an optimum total amount of taper per unit length of pile is about one-half inch per foot of vertical length. For example, if a pile is designed with an about 14 inch square butt and an about 7 inch square tip, and about feet of tapered tip section, the pile will be about the optimum amount of taper.

It has also been found that reinforced concrete piles which have tips of area of less than about 6 in. square, have an increased tendency to crack, break, or spall, so that it is desirable to make and use piling having tipped dimensions of not less than about 6 in. square, and preferably not less than about 7 in. square. Piles having tips of area greater than about 6 in. square, better withstand variations in pressure during driving, and have greatly reduced tendencies to break and turn out of their intended vertical path.

In practice, the square, reinforced or prestressed concrete tapered piling of the present invention is typically most advantageously used on construction sites wherein the earth comprises a variety of strata of different compositions and densities. For example, as illustrated in FIG. 1, the surface soil strata may comprise a relatively light density soil, and as the pile penetrates the surface strata it may encounter other strata which are more or less dense than the surface strata. The use of pilings is necessary in the first place because the surface strata is of insufficient density and stability to support the structure which it is desired to built upon the construction site. It is therefore an essential object of pilings to provide a load-bearing capacity which is greater than the natural load-bearing capacity of the surface strata by penetrating the less dense earth strata and reaching earth strata at depths which strata have greater density and provide sufficient load-bearing capacity for the pile.

In some building sites, the earth strata may be such that the upper layers of soil have insufficient loadbearing capacity, and higher density layers of higher load-bearing capacities are located at greater depths. In such soil conditions, straight sided piles which provide point-to-point support from the area of the tip to the corresponding area of the butt surface, achieve desired load bearing capacities only by being driven to the more dense strata located at greater depths. For example, in the state of Florida, building sites are found where there is generally a strata of relatively low strength limestone at about minus 10 to feet, and under the limestone there is sand to about minus 50 to 60 feet. Only at about minus 60 feet are rock strata encountered which are generally strong enough to provide sufficient point-to-point load-bearing capacity. One will readily appreciate the large lengths of piling material necessary to drive this great distance, as well as its attendant expenseStraight-sided pile, in particular, will typically readily penetrate less strong layers, such as the aforementioned limestone strata, and in doing so will break up and weaken those strata throughout the construction site. In some cases the straight-sided pile may even penetrate the lower rock strata.

However, by using the advantageous square, rein forced or prestressed, solid concrete tapered pilings of the present invention, surprisingly it has been found that even in construction sites where the soil strata appear insufficiently strong to provide to straight-sided piles the desired load bearing capacity, the inventive piles (of the same butt area) provide the necessary load bearing capacity, while at the same time greatly reduce the necessary length of the piling. In addition, the inventive piles are more easily and quickly driven to a designed load capacity. In an industry where driving costs are given in cost per driven foot, the inventive pile achieves great savings in driving costs as well as in material costs, while providing more than the design criteria load-bearing capacity. In addition, the shorter piles allow the use of standard rather than extended height driving equipment, and thereby eliminate punching a starting hole, sometimes required by long pilings, and dangerous and often destructive whipping of long lengths of piling during driving. Furthermore, in most applications, a shorter unitary piling may be used thereby eliminating the need for splicing additional lengths together and thereby obviating the more questionable load-bearing and uplift anchorage capacities of spliced pilings.

Even more surprising is the fact that the significantly shorter tapered piles of the present invention also provide more than the design criteria uplift anchorage capacity, thereby providing structures supported by such pilings, the necessary support and stability to firmly anchor them against the potentially destructive forces of wind, currents, or waves. Uplift anchorage capacity is explained with reference to FIGS. 4 and 5, wherein a building structure which is illustrated having a foundation 31 which is supported by the inventive piles 32. Walls 33 are referred to as stress walls or shear walls and are illustrated in the configuration of a giant I beam. These walls are useful structural exterior and partition walls within the building itself, but when considered in their shear wall configuration, form a giant structural I-beam which is vertically secured to the foundation of the building. The shear wall construction provides the structure with lateral stability and support against external forces such as winds, currents, or waves, as indicated by arrows W.

As illustrated in FIG. 5, external forces W have a tendency to produce great leverage to pivot the structure around the opposite lower comer 34 of its foundation 31. Such forces may be quite great when the area of the side wall of a building is considered in conjunction with the force per unit area of strong winds, currents, or waves, as well as the effective leverage distance from the point or axis about which the structure has a tendency to pivot. Arrows 35 and 36 therefore schematically indicate the directions of the effective resultant components of force caused by a force such as wind force W urging a building structure 30 in a direction D wherein the shear walls 33 of the building would effectively be pivoted about a point or axis 34. The pilings 32 upon which the foundation 31 is formed, and especially those pilings which are at the greatest distance from the axis about which the potentially destructive external forces are attempting to push the structure, must be sufficiently anchored in the earth strata below the construction site so that they more than adequately counteract the uplift force in direction 36 caused by the external force of wind, currents, or waves. Typically, straight-sided piling will be much longer than the advantageous tapered pilings of the present invention, and therefore will themselves have a greater weight to counteract uplift forces. However, the advantageous piles of the present invention surprisingly provide an uplift capacity which is substantially greater than the uplift anchorage capacity of the longer straight-sided piles of similar load bearing capacity.

Although the surprising load-bearing capacity and uplift anchorage support provided by the present invention, are not fully understood, it is believed that a number of things take place when the inventive tapered piles are driven in a building site which would previously not support the desired load with straight sided piles of such short length. For example, it-is believed that as the advantageous tapered piles are driven into the earth strata, that the tapered side portions 14 compact the soil in directions 21 laterally from the axis of the piling, and thereby increase the density of the soil into which the pilings are being driven. The compacting of the soil .tends to increase the load bearing capacity of the soil strata, and tends to increase the frictional forces between the surface of the pile and the strata into whichit is driven. Of course, the earth strata directly under the tip 16 of the tapered pile is pushed aside and compacted as the piling is being driven into the earth. 'In the inventive pile, the tapered sides also support some of the load placed upon the piles because the tapered sides laterally distribute components of load forces placed on the pile in the direction of its central axis'Thus surprisingly, a tapered piling of the same butt area as a straight sided piling, will support a greater load at a lesser depth and on less dense strata than the straight piling driven into similar strata. Apparently the compacting effect of driving the tapered piling very greatly and unexpectedly enhances the load bearing capacity of the tapered piling and the soil strata in which it is driven. The compacting effect of the tapered pile also unexpectedly greatly increases the uplift anchoring characteristics of the tapered piling apparently because the compacted and more dense soil surrounding the tapered pile moretightly adheres to the surface of the pile, thereby increasing the force necessary to remove the pile from the hole produced by the pile when it is originally driven. The advantageous compacting effects are even further enhanced when the inventive tapered pilings are driven in clusters as is the common practice. Conversely, straight piles in clusters continue to break up and weaken the more shallow strata, as already discussed herein. The tapered pilings not only enhance the load-bearing capacity of the earth strata in the site, but also simultaneously automatically seek the desired load capacity in the densified strata.

Apparently because of the advantageous soil compacting which occurs when the inventive tapered pilings are driven, the tapered pilings may be driven on a construction site in close proximity with straight sided pilings, and have the advantageous effect of increasing the load bearing capacity of straight sided pilings in the site. When used in this combination, the tapered pilings and straight sided pilings should be driven at distances not greater than about 6 ft. from each other. Because of the increased load bearing capacity of the earth strata in the site when tapered pilings are driven therein, the straight sided pilings may achieve increased load capacities with shorter pile length.

In addition to the other advantageous characteristics of the tapered pile, tapered piles have been found to drive to a desired load-bearing capacity faster than straight-sided piles of the same butt area. Also because of the greatly decreased length of the tapered piles, the total number of blows necessary to reach the desired load capacity is significantly reduced over the larger straight sided piles, thereby realizing significant sanvings in construction costs.

One familiar with the use of pilings in construction sites will knowthat the determination of what type of piling and especially what length of piling'should be used in a given site is typically made with the help of tests such as test borings and test pile drivings.

The following examples specifically define various preferred embodiments of the inventive tapered piles and methods of using said piles.

EXAMPLE I A 35 ton capacity solid reinforced and prestressed concrete tapered pile is manufactured by providing a concrete mold everywhere having a squarecrosssection substantially perpendicular to the longitudinal axis of the mold which includes a straight-sided butt mold section, and a tapered sided tip mold section wherein each of the four tapered sides converges toward the axis of the mold from a shoulder joining the butt mold section and the tip mold section at arate of taper of about one-fourth in. per linear foot of axis. The tip surface of the tip mold is about 7 in. by7 in. square, and the cross-section of the butt section and the butt surface are about 14 in. by 14 in. square. The tapered tip molded section is about 15 ft. long and the butt section may be of any suitable length. Within the mold four seven-sixteenths in. steel reinforcing strands are placed for prestressing and reinforcement at locations located inwardly about 2 in. from the adjacent sides of the butt surface, and the adjacent sides of the tip surface, and four more similar strands may be placed therein with their ends located along the sides of the square cross section defined by the four original wires.

The strands in the corners are tensioned for prestressing at an initial pull of about 18,900 lb. The concrete mold is then filled with concrete suitable for providing structural characteristics including a cylinder strength at release of about 3,000 p.s.i. and a cylinder strength at driving (f'c) of about 5,000 p.s.i.

EXAMPLE n The advantageous tapered pile of the present invention was compared to a standard straight-sided pile in comparative tests on three locations at Miami, Florida. Standard test borings on all three test areas revealed that the three areas had somewhat different earth strata. The test boring results showed that Area No. 1 would be a preferred building site over Area No. 2, which would be a preferred building site over Area No. 3.

Each of the areas had an about 5 ft. layer of fill overlying a layer of organic clayey silt overlying a layer of sand overlying a layer of limerock. Therebelow various layers of limerock or limerock and sand, or sand alone, were encountered and cochina bedrock was under all three areas at depths of 45 to ft. ln Area 1, the first and most significant layer of limerock occurred at a lesser depth than the other sites, and in Area 1, an about 2 ft. thick layer of cochina rock occurred at a depth of about 24 ft. The mostsignificant area of limerock occurred at a slightly higher level in Area 2 than in Area 3, and the bedrock cochina occurred at a higher level in Area 1 than in Area 2, wherein it occurred higher than in Area 3.

The following types of concrete piles were driven during the tests:

Pile Type A Straight-sided 14 in. square prestressed concrete, 40 ft. long, with a concrete compressive strength of 5,000 lb/in. and reinforced with four seven-sixteenths in.

steel strands. This pile is a standard 35 ton capacity concrete commercial pile. The load bearing capacity of the pile as a structural member is rated at 98 tons.

Pile Type B Tapered precast concrete, 25 ft. long, reinforced with four No. 7 rebars. The pile tapers from a 6 in. square tip to an 18 in. square butt over a distance of 24 ft. (width increase at rate of 0.50 in/ft), with a 1 ft. long l4 in. square splicing stub at the butt end.

Pile Types A and B were extended by splicing with one or two (as required) 18 ft. long Type A extensions. The splice consisted of a 1 ft. long four-sided welded steel box, with inside dimensions of about 14.5 in. square. The splice was placed over the butt end of the driven pile and received the bottom of the pile extension. Reinforcing bars welded horizontally on the inside faces of the steel box prevented the splice from sliding along the pile. Two one-half in. thick plywood cushion blocks were placed between the ends of the pile and the extension to reduce damage to these portions of the pile.

All pilings driven in the test were driven by a Link- Belt 520 diesel hammer, with a rated energy of 26,300 ft/lb.

in order to compare the driving performance of the tapered and straight-sided piles, pile Types A and B were driven to resistances greater than typically required for 35 ton formula pile capacity. Driving of these pile types was continued until practical refusal was obtained at afinal resistance of about to blows/in, (hereafter bl/in) until the pile butt was damaged (spalled or shattered concrete), or until the pile butt drifted off location causing the pile to tilt. In order to drive the piles to refusal, all but one of the Type A and B piles were lengthened by splicing Type A pile extensions to the driven pile as previously described.

The driving resistance was calculated as follows: The net driving resistance for a 35 ton pile driven with a 26,300 ft-lb hammer is about 19 bl/ft (blows per foot). The average resistance encountered while driving through the overburdened above the limerock, which averaged about 10 bl/ft for the Type A and B piles,

-must be added to the net driving resistance to obtain the gross driving resistance. Consequently a 35 ton pile would have to be driven to a minimum final resistance of 29 bl/ft.

The test piles were driven to depths at which driving resistances were at least equal to the gross required resistance for a minimum of 3 consecutive ft.

Evaluation of the driving records using the criteria of 3 consecutive ft. of 29 bl/ft or greater driving resistance indicates that the desired bearing for the straight-sided Type A and heavily tapered Type B piles was obtained at the following elevations:

If all piles were driven from surface el +4, the following average lengths of piles would be required at the three test driving areas.

The last column indicates the savings of pile length achieved by .using Type B Tapered piles instead of Type A Straight-Sided piles. It is therefore apparent that the tapered Type B piles can obtain the required bearing at a much higher elevation (therefore requiring shorter piles) than the straight-sided Type A piles. At the three test driving areas, the required lengths of the tapered piles averaged about 51 per cent less than the required length of the straight-sided piles driven to the same criteria.

EXAMPLE llI Comparative tests of the advantageous tapered pile and straight-sided pile were driven at North Ft. Lauderdale, Florida, using a design criteria of ton capacity. Straight pile were driven to 54 feet and 70 feet, respectively. Test loads applied to the test pile revealed that the 54 ft. depth of the straight pile was adequate for the design criteria of the pile. However, the straight pile driven to the 70 ft. depth failed to attain the design criteria load, presumably because of the erratic lower strata at the test site. At the same test site 28 ft. tapered pile having the same cross-sectional butt area were driven. The same test loads were applied to the 28 ft. tapered pile, which supported a load of over 140 tons with per cent recovery.

EXAMPLE IV in. per foot from the 14 in. by 14 in. straight section to the 7 in. by 7 in. tip through a tapered distance of about 15 linear feet. In the same locality, the tapered pile and the straight pile having a uniform 14 in. by 14 in. square dimension were driven with identical loads. The tapered pile drove to the point of refusal at about 17 ft. 0 in. The straight pile drove to a comparable point of refusal at about 41 ft. 0 in. Load capacity and tension tests made on the tapered pile showed that the tapered pile had a load-bearing capacity of 147 tons and an uplift tension support capacity of 69 tons. While the straight sided pile achieves its designed load bearing capacity, it failed in uplift tests at about 20 tons.

Although specific components, steps, and proportions have been stated in the above description in order to explain the nature of the invention to those skilled in the art, it will be understood that other suitable materials, steps, and details in, or uses for, the present invention may be made with various satisfactory results, and such changes are intended to be included within the principles and scope of this invention.

What is claimed is:

1. A reinforced solid concrete pile everywhere having a square cross-section, comprising: a straight sided butt section having a cross-section of at least 14 inches square, and a tapered-sided tip section the widest portion of which has the same cross-sectional dimensions as said butt section, and wherein each of the four tapered sides of said butt section converges, from a shoulder joining said butt section toward the longitudinal axis of the pile an amount in the range of about oneeighth to about three-eighths inch per linear foot of axis, said taperedtip section being not less than about 9% feet long, and terminating in a tip end comprising a square area not less than about 7 inches square.

2. The pile of claim 1 where each of the tapered sides converges toward the axis at about one-fourth inch per linear foot of axis.

3. The pile of claim 2, wherein the tapered tip section is about 15 feet long.

4. A method of increasing the load bearing capacity and uplift anchorage capacity of piles of constant butt cross-sectional area driven in the same construction site, comprising i providing tapered pilings of reinforced, solid concrete, everywhere having a square cross-section, said tapered pile comprising a straight-sided butt section having said constant cross-sectional area of at least 14 inches square, and a tapered-sided tip section the widest portion of which has the same cross-sectional dimensions as said butt section, and wherein each of the four tapered sides of said tip section converges from a shoulder joining said tip section to said butt section, toward the longitudinal axis of the pile an amount in the range of about one-eighth to about three-eighths inch per linear foot of pile axis, said tapered tip section being not less than about 9% feet long, and terminating in a tip end comprising a square area not less than about 7 inches square, and

driving said tapered pilings thereby simultaneously densifying the composition of said strata and achieving a driven point of refusal commensurate with a desired criteria load bearing capacity and uplift capacity.

5. The method of claim 4, wherein the step of providing said tapered pilings comprisesproviding a tapered pile wherein the tapered tip section is about 15 fee long.

6. The method of claim 4, additionally comprising building a designed structure on said tapered pilings driven at said site, thereby providing at least said desired criteria load bearing capacity and uplift anchorage capacity'for said structure.

7. A method of increasing the load bearing capacity and uplift anchorage capacity of straight-sided piles driven in a construction site, comprising,

driving straight sided pilings and tapered pilings in close proximity to each other in said construction site, each of said tapered pilings comprising:

. a reinforced solid concrete pile everywhere having a square cross-section, comprising: a straight sided butt section having a cross-section of at least 14 inches square, and a tapered-sided tip section the widest portion of which has the same'cross-section dimensions as said butt section, and wherein each of the four tapered sides of said butt section converges, from a shoulder joining said butt section, toward the longitudinal axis of the pile an amount in the range of about one-eighth to about threeeighths inch per linear foot of axis, said tapered tip section being not less than about 9% feet long, and terminating in a tip end comprising a square area not less than about 7 inches square.

8. The method of claim 7, wherein said straight sided piles and tapered pilings are located not more than about 6 feet apart.

9. A reinforced solid concrete pile everywhere having a square cross-section comprising, a straight sided butt section having a cross-section about 14 inches square, and a tapered-sided tip section the widest portion of which has the same cross-sectional dimensions as said butt section, and wherein each of the four tapered sides of said tip section converges, from a shoulder joining said butt section, towardthe longitudinal axis of the pile an amount of about one-fourth inch per linear foot of axis, said tapered tip section being about 15 feet long, and terminating in a tip end about 7 inches square. 

1. A reinforced solid concreTe pile everywhere having a square cross-section, comprising: a straight sided butt section having a cross-section of at least 14 inches square, and a tapered-sided tip section the widest portion of which has the same crosssectional dimensions as said butt section, and wherein each of the four tapered sides of said butt section converges, from a shoulder joining said butt section toward the longitudinal axis of the pile an amount in the range of about one-eighth to about three-eighths inch per linear foot of axis, said tapered tip section being not less than about 9 1/3 feet long, and terminating in a tip end comprising a square area not less than about 7 inches square.
 2. The pile of claim 1 where each of the tapered sides converges toward the axis at about one-fourth inch per linear foot of axis.
 3. The pile of claim 2, wherein the tapered tip section is about 15 feet long.
 4. A method of increasing the load bearing capacity and uplift anchorage capacity of piles of constant butt cross-sectional area driven in the same construction site, comprising providing tapered pilings of reinforced, solid concrete, everywhere having a square cross-section, said tapered pile comprising a straight-sided butt section having said constant cross-sectional area of at least 14 inches square, and a tapered-sided tip section the widest portion of which has the same cross-sectional dimensions as said butt section, and wherein each of the four tapered sides of said tip section converges from a shoulder joining said tip section to said butt section, toward the longitudinal axis of the pile an amount in the range of about one-eighth to about three-eighths inch per linear foot of pile axis, said tapered tip section being not less than about 9 1/3 feet long, and terminating in a tip end comprising a square area not less than about 7 inches square, and driving said tapered pilings thereby simultaneously densifying the composition of said strata and achieving a driven point of refusal commensurate with a desired criteria load bearing capacity and uplift capacity.
 5. The method of claim 4, wherein the step of providing said tapered pilings comprises providing a tapered pile wherein the tapered tip section is about 15 feet long.
 6. The method of claim 4, additionally comprising building a designed structure on said tapered pilings driven at said site, thereby providing at least said desired criteria load bearing capacity and uplift anchorage capacity for said structure.
 7. A method of increasing the load bearing capacity and uplift anchorage capacity of straight-sided piles driven in a construction site, comprising, driving straight sided pilings and tapered pilings in close proximity to each other in said construction site, each of said tapered pilings comprising: a reinforced solid concrete pile everywhere having a square cross-section, comprising: a straight sided butt section having a cross-section of at least 14 inches square, and a tapered-sided tip section the widest portion of which has the same cross-section dimensions as said butt section, and wherein each of the four tapered sides of said butt section converges, from a shoulder joining said butt section, toward the longitudinal axis of the pile an amount in the range of about one-eighth to about three-eighths inch per linear foot of axis, said tapered tip section being not less than about 9 1/3 feet long, and terminating in a tip end comprising a square area not less than about 7 inches square.
 8. The method of claim 7, wherein said straight sided piles and tapered pilings are located not more than about 6 feet apart.
 9. A reinforced solid concrete pile everywhere having a square cross-section comprising, a straight sided butt section having a cross-section about 14 inches square, and a tapered-sided tip section the widest portion of which has the same cross-sectional dimensions as said butt secTion, and wherein each of the four tapered sides of said tip section converges, from a shoulder joining said butt section, toward the longitudinal axis of the pile an amount of about one-fourth inch per linear foot of axis, said tapered tip section being about 15 feet long, and terminating in a tip end about 7 inches square. 